Installing a small MHVR system

[Mark-R]

I'm new to this blog. I'm lifelong DIYer and had a lot of hands-on involvement with the construction of my current house which is now 6yrs old. This included the installation of a MHVR system (then designed by my builder) based around a Sentinel Kinetic in the basement and using taped 125mm plastic pipework throughout. Whilst balancing seemed rather haphazard when it was commissioned, in terms of performance including quiet, I have absolutely no complaints. 

 

This experience has spurred me on to consider self-installing a simple system for my daughter and her family. Their house is a completely different kettle of fish- built in the 1960s of modest size with total floor 105 sqm and  ceiling height 2.2m, it has a very large amount of glazing including several floor to ceiling picture windows. Its double glazing is in good nick but there are no trickle vents, has modern external doors (not PH, not that modern) and apart from the extractor over their gas hob, has no ventilation (none in the bathroom). It was never built to a standard approaching air tight. Despite dehumidifiers it is a condensation and mould nightmare. It feels stuffy unless you open the windows, which are large and let all the heat out. The purpose of a system here would be first to help with air quality. I have no expectations of any significant heat recovery. Nevertheless, as a home it is a long term prospect for them, with potential for extension and other improvements, so the greater financial investment seems more reasonable.

 

The only feasible location for the  MHVR unit is in part of a large built-in wardrobe in a bedroom that is rarely used. This would allow easy access for maintenance, good access to a suitable external wall for connections to outside and well placed for a radial system of piping to the other rooms via the loft space, and down to the lounge and dining room on the ground floor. The loft is outside the heated envelope but it should be feasible to bury pipework beneath the considerable insulation there.

 

I would be grateful for any general observations from experience. I also had several specific questions:

 

There is a dazzling variety of machines on the market. I am thinking of a Titon HRV1.25 Plus. This seemed a good option in terms of size, cost and not being over-engineered for the job I'm asking it to do. Does anyone have any experience of these units? or would recommend others of similar size/output? It would hang on a wall. Is that a recipe for vibration noise? If so, any tips to mitigate this?

 

Although I expect to use radial 75mm flexible ducting on the input side, because of the layout, I could install larger hard plastic ducting, eg 125mm diameter, on the extract side as it only has to do kitchen and bathroom, which might be cheaper and lead to less work for the machine, so perhaps also quieter. I would balance the system by adjusting the ceiling fittings. Any reason not to use dissimilar ducting on the two sides?

 

The Titon info suggests connecting pipes (125) directly to the machine but I am sure I have read somewhere that it is generally a good idea to use a short length of flexible corrugated duct between the array and MHVR unit for maintenance or replacement. We did this with my own house. I guess I could use BPC Ventilation Flexible Acoustic Silencers here. Have I mis-remembered this recommendation?

 

Thanks. 

 

 

 

 

 

 

[Mike]

Welcome to the forum - an interesting challenge.

 

20 minutes ago, Mark-R said:

The only feasible location for the  MHVR unit is in part of a large built-in wardrobe in a bedroom that is rarely used.

What's wrong with the loft? A loft / garage / kitchen (or anywhere else) would be preferable, even if the bedroom is little used. Not that MVHR is very noisy, but at night noises seem louder, and I'd not consider it myself.

 

It may be better to wait and incorporate it into one of those future extensions you mention. Unless you can easily swap the hot water tank into the wardrobe & put the MVHR where that is - probably unlikely though.

 

30 minutes ago, Mark-R said:

or would recommend others of similar size/output?

For efficiency, the best place to look is https://database.passivehouse.com/en/components/list/ventilation_small? - the Efficiency Ratio is the most important number, but not the cheapest units.

 

32 minutes ago, Mark-R said:

It would hang on a wall. Is that a recipe for vibration noise? If so, any tips to mitigate this?

It's good if it's a solid wall. (Over)sizing the unit so it runs at low speed is a good way of minimising noise in general.

 

36 minutes ago, Mark-R said:

Any reason not to use dissimilar ducting on the two sides?

Not in principle.

 

38 minutes ago, Mark-R said:

it is generally a good idea to use a short length of flexible corrugated duct between the array and MHVR unit for maintenance or replacement.

Very short lengths - just enough to undo the connection - are OK. Not sure that many people do it though.

 

45 minutes ago, Mark-R said:

apart from the extractor over their gas hob

Swapping the gas hob for electric would significantly improve the air quality.

[G and J]

From what I’ve read (yep, I’m yet another poster who masks guesswork with confidence) MVHR is only energy efficienct if a fairly good level of air tightness is achieved.  
 

That would seem to indicate that a centralised system is not ideal. Reducing humidity is likely to increase the heating bill whatever system you go for but in your position I’d look at things like extractors or dmev. Nowhere near as sexy but cheaper and easier methinks. 

[Mike]

50 minutes ago, G and J said:

MVHR is only energy efficienct if a fairly good level of air tightness is achieved

True, and improving airtightness should be a priority where feasible. But efficiency doesn't have to be the objective, particularly if rooms are stuffy with mould growing, though there are indeed other options apart from MVHR.

[Iceverge]

Those flexible silencers aren't great. I would use a rigid metal one in preference. 

 

Another option if there is no solid wall for the MVHR unit is just to sit it on the ground floor on rubber feet or a matt. 

 

Mechanic ventilation with or without heat recovery is always worth it regardless of airtightness levels. True it won't do much on a leaky house on a windy day but it will serve a valuable function on days with no wind in keeping the interior healthy. dDCV is cheap and easy to install if you can live with out HR.

[JohnMo]

So the real issue is no proper ventilation. Not sure MVHR is the answer. MVHR is really for energy saving when you have done everything else. You will be spending £2 to 4k on hardware and plus if paying for getting it installed, not really getting benefits from heat recovery, so why bother. Plus pumping air in and of the property on a continuous basic (electric) plus replacement filters.

 

A more practical solution is MEV or simply do dMEV. A fan in each wet room, run 24/7 and only boosts when needed. You need either trickle vents in dry rooms or a through wall vent. These should ideally modulate themselves open or closed based on humidity.

 

Get the following fans, they are silent, they auto boost only when needed and only need power no need fir switching boost etc. Greenwood CV2GIP, you can get for £70 on eBay. They draw between 1 and 3W when running.

 

Then something like this is the dry rooms, https://www.bpdstore.co.uk/glidevale-fresh-99h-humidity-sensitive-wall-ventilator/p/231 as you have no trickle vents.

 

The other thing to do is undercut (6 to 10mm) the internal doors to allow cross ventilation with the doors shut.

 

Less than a £1k, the saving will pay for a lot of energy. Plus demand based dMEV looses very little heat, the vents basically close down with no one in the room.

[Iceverge]

Those CV2GIP fans are excellent. Thakd for the tip @JohnMo

 

Thinking about the categorisation I would split Mechanical extract ventilation (MEV) into 3 categories. 

 

1. Intermittent extract fans such as those annoying noisy bathroom fans we all hate. 

 

2. CEV continuously extract ventilaton that run at a constant level all the time. 

 

3. DCV Demand Controlled Ventilation that adjust the a airflow according to demand based on CO2 or humidity. 

 

Then add a small "d" to indicate a decentralised version. 

 

I would say the Greenwood CV2GIP is a dDCV. 

 

Would you agree/disagree? 

 

 

 

 

[JohnMo]

I would agree, but industry would call the dMEV. But they are really dDCV, when coupled with humidity controlled inlets

 

1. Intermittent - yes hate them, they are generally very poor performing especially generic builders merchant ones. Lots of noise, not much flow.

 

 

[Iceverge]

Another example of Buildhub being a decade ahead of Industry. 

[Mark-R]

Thank you - that's all really helpful, and pause for more thought. 

I certainly will look at the alternatives you have outlined.

I think a system which, once set up, does involve them actively managing it will suit them as they are not technically minded.

 

A couple of other thoughts:

Where one has a choice presumably the DDCV units should extract to a sheltered wall?  and internally, sited as far from the door a possible.

The same would apply to the humidity sensitive wall ventilators?

One of the DG units in a bedroom window is misting and will need replacement. If they changed the window surround they could change to a trickle vent type. Its there anything to choose between this and installing a humidity sensitive wall ventilator instead?

I've only seen manually adjusted trickle vents but I imagine there might be humidity driven ones (££?) now. 

 

Thanks again

 

 

[JohnMo]

The fan can go through any outside wall or through ceiling and out the eaves. Ideally as far away from door as possible. You do not have a ventilator or trickle vents in wet rooms.

 

Same with wall ventilator. 

 

Trickle vents or wall ventilator do exactly the same thing.

 

Manual trickle vents are not the same, the home owner will just close them and 6 months later say they are drafty and say oh, look I have mould no idea why.

 

There are many makes, some with noise reducing measures etc. 

 

Whole thing that makes the system work is cross ventilation.

 

If the double glazing unit is misting between the glazing it's broken. If it's just misty on the inside after a night's sleep, the ventilation is really poor. 

[MJNewton]

19 hours ago, Mark-R said:

I would be grateful for any general observations from experience.

 

Hi Mark, welcome to the forum.

 

We retrofitted MVHR (also a Titon HRV1.25 as it happens) and have been really pleased with it. In our case it was a 125m²  2007-built property and whilst we didn't have any condensation/mould issues to treat the initial motivation was the creation of an open plan kitchen which, primarily for aesthetics, we didn't want much on the walls (high level cupboards and, more relevant to this discussion, a hob extractor) and so started exploring the use of MVHR.

 

Retrofitting was difficult, particularly given we're spread over three floors, although saying that we've ended up with a pretty much 'invisible' installation and so looking back it was really just a lot of planning, problem solving and head scratching but we got there in the end. We were helped massively by the flooring structure being long engineered I-joists which, surprisingly given my usual luck, nearly all happen to run in the ideal direction for us! Furthermore, given we had the ceilings down on most of the ground floor that also helped. To keep costs down we actually bought the MVHR unit off eBay for £350 as a second-hand unit albeit one that had only been installed and not used as it was one of many fitted to a small estate of houses that turned out to not be to specification so were pulled out and replaced. It still ended up costing us £1400 in total once every last component is factored in.

 

It's been in around five years now. Electrical running costs have been ~£26/yr (based on today's rates of 22p/kWh and ~125kWh/yr consumption) and I change the filters every 6 months at around £1 a time as the frames are reusable so I just buy a square meter of filter medium to chop up. Performance in terms of humidity control and perceived air quality has been excellent. We also saved £400 in not having to have trickle vents in the lift-and-slide doors too which was a nice bonus.

 

Based on our experience I would definitely recommend it, but it would certainly be worth exploring the alternative options raised for consideration by others above.

Edited October 11 by MJNewton

[JohnMo]

1 hour ago, MJNewton said:

We also saved £400 in not having to have trickle vents in the lift-and-slide doors too which was a nice bonus.

£400 for trickle vents, not anyone sane would accept that.

[MJNewton]

7 minutes ago, JohnMo said:

£400 for trickle vents, not anyone sane would accept that.

Yeah I thought it was a bit steep, but I was assuming it was just to cut holes in the frames and whack some form of louvres/shutters over the top but it turns out to have been for a separate fabricated section that would be fixed to the top of the frame. 

[Iceverge]

We have MVHR in the house a PROAIR 600pli unit. Filters are not cheap at about €22/pair but the unit is fine. I change them every 6 months. 

 

I did dismantle it to give the insides a clean after about 2 years. I think I may do the same and change some bearings this year after 4 years operation. I wouldn't say it would be unreasonable to allocate £100/year in maintaining, servicing and running the unit if you were outsourcing the job. It recovers many times more than that in energy for us but more importantly it gives healthy and comfortable internal air. 

 

The dDCV I have out in the office is a plug in, pick your setting and completely forget. No heat recovery but then it was about £60 from eBay. You can hear it if you are beside it. I would compare the noise to a PC fan on tickover. I wouldn't put it beside a bed but it would be inaudible in an adjoining room.

 

[JohnMo]

9 minutes ago, Iceverge said:

The dDCV I have out in the office is a plug in, pick your setting and completely forget. No heat recovery but then it was about £60 from eBay.

Our Greenwood CV2GIP, is in our garden room, also, it was also £60 on eBay. It is set on min speed, and completely inaudible. We originally had another make and it was quite noisy.

 

Only thing I have done is take the front cover off to see if it was still running - which it was.

[mickeych]

We haven't designed in a specific level of air-tightness to this old stone barn conversion and the target was initially 'just lower than 5,' but we are sold on centralised MVHR for air quality and was hoping for some HR. But reading the advice regarding HR and airtightness correlation, I am thinking that we need to revisit our levels of airtightness. Is it worth trying to improve airtightness with https://www.aerobarrieruk.co.uk/ or is it unlikely to make a huge difference long term?

[Iceverge]

I would say Aerobarrier is likely to be very effective. If you use the search function on here there's a couple of people who have used it. It won't fix bad windows and doors however and if you have designed holes like badly fitted stoves it can't fix that either. 

 

I wouldn't get too caught up with ACH numbers and MVHR effectiveness, as it's largely an academic argument about energy recovery on a windy day.

 

On a calm day it'll perform much the same in any house. You'll get the comfort and benefits regardless. 

 

The only situation I wouldn't think it's worth it is if you need to do mega destruction of a perfectly ok house to install, as the alternative of dDCV is so cheap and easy. 

 

 

 

 

[Nickfromwales]

5 hours ago, mickeych said:

We haven't designed in a specific level of air-tightness to this old stone barn conversion and the target was initially 'just lower than 5,' but we are sold on centralised MVHR for air quality and was hoping for some HR. But reading the advice regarding HR and airtightness correlation, I am thinking that we need to revisit our levels of airtightness. Is it worth trying to improve airtightness with https://www.aerobarrieruk.co.uk/ or is it unlikely to make a huge difference long term?

1,000,000% It'll be the best time/effort/money you spend (IMHO). I promote airtightness over insulation every day; with a house that has MVHR obvs.

[Mike]

On 23/10/2024 at 22:09, Nickfromwales said:

I promote airtightness over insulation every day

Yes, it's a cheap win. Heat is typically lost through insulation over the course of days, but is lost through air leakage within minutes or hours.